I. Field of the Invention
This invention relates to a method and apparatus for driving pins into rock faces in mines to prevent their collapse.
II. Description of the Prior Art
The collapse of sections of mine roof has long been regarded as one of the greatest hazards of undergound mining, and various methods of supporting the overburden in mines have been tried.
The roof of a mine generally consists of rock strata, wherein the strata vary considerably in their strength and resistance to collapse when their natural underlying support is removed by mining. It has long been known that such a mine roof can be considerably strengthened by bolting or pinning.
Bolting is generally accomplished by drilling into the overhead strata and inserting a metal bolt carrying a bearing plate. The bearing plate may comprise one or more large metal washers, pieces of wood, metal, or combinations of these to provide a bearing surface between the bolt head and the supported rock. The bolt preferably extends well into a strong stratum and is held securely by one of several means, such as by splitting and expanding its end with a wedge when the bolt is forced into the hole by mechanical type anchors or by cementing the bolt in place by the use of quick setting polymerizable resins or cement.
These methods provide more mine area for the moving of men and equipment, and offer many advantages over the earlier methods of timbered supports. They permit the mining of pillars of valuable material which might otherwise be left to serve as structural support.
More recently, considerable success has been achieved by forcing metal pins into the rock under high pressure, generally developed by hydraulic means. This, and related techniques are receiving special attention in recent years, particularly in view of the Federal Coal Mine Health and Safety Act of 1969 because of the dust control and noise level standards which it contains, for the drilling of the roof of a mine for the insertion of roof bolts is both dusty and noisy. This recently developed method of driving pins into the roof by sheer force is, however, generally confined to the use of relatively short pins, for example, in the order of 24 inches in length or less, whereas it is sometimes advantageous to use pins up to 7 feet in length in order to reach a stratum having the desired strength or to unite into one roof structure, strata extending upward from the roof for several feet.
A pin-set machine which drives the pin into rock by sheer force tends to bend and distort the pins becuase of the very high pressures required. This can place an upper limit on the length of pins that can be employed. Such a machine also tends to shatter the rock about the pin, so that the pin can be extracted from its position with less force than would be required if this local shattering action had been avoided.
Although collapse of the roof of a mine is a major hazard which can be substantially eliminated by roof pinning, this technique can also be used to advantage in the "rib" or sidewall of a mine, for in certain mining operations, as for example, in the mining of natural trona, large slabs sometimes split off the rib. These slabs are dangerous to personnel, as well as disruptive, often damaging machines, or holding up mining operations until a passageway can be cleared. A pin-set machine having the versatility to drive pins into the rib, as well as into the roof of a mine, would offer advantages over one applicable only to roof pinning operations.